Heart valve disease continues to be a significant cause of morbidity and mortality, resulting from a number of ailments including rheumatic fever and birth defects. Currently, the primary treatment of aortic valve disease is valve replacement. Worldwide, approximately 300,000 heart valve replacement surgeries are performed annually, many involving mechanical heart valves composed of rigid, synthetic materials while the rest receive bioprosthetic heart valves which utilize biologically derived tissues for flexible fluid occluding leaflets. In general, bioprosthetic valve replacements have good hemodynamic performance and do not require the anticoagulation therapy necessary for mechanical heart valves.
Flexible leaflets used in heart valves are typically made from bioprosthetic homograft or xenograft materials. For example, the most successful bioprosthetic materials are whole porcine valves and separate leaflets made from bovine pericardium stitched together to form a tri-leaflet valve. In addition, flexible leaflets formed of polymeric, fiber-reinforced, and other synthetic materials have been proposed. The most common bioprosthetic valve construction includes three leaflets mounted around a peripheral support structure with free edges that project toward an outflow direction and meet or coapt in the middle of the flowstream.
Aortic stenosis is abnormal narrowing of the aortic valve characterized by a significantly higher than normal pressure gradient across the aortic valve. It follows that an important characteristic of a replacement aortic valve is minimal aortic pressure gradient, typically attained by increasing the effective orifice area through the valve. Solutions include placement of the prosthesis (sub-annular, intra-annular and supra-annular) in order to implant a prosthesis with the largest possible effective orifice area. Supra-annular placement (where the sewing cushion lies above the aortic annulus) is often preferred because usually a valve with a larger internal orifice diameter can be implanted. However, in patients with small aortic roots, either due to anatomy, physical stature, or severe calcification, only the smallest-sized valves (e.g., 19 mm) may be used. Sometimes an even smaller valve would be desirable, but valves smaller than 19 mm are not commercially available. Moreover, even with a supra-annular implant, the valve often does not maximize the flow orifice area.
In view of actual and perceived drawbacks associated with current bioprosthetic heart valves, a valve with an increased effective orifice area for a given valve size is desirable.